The present exemplary embodiment relates generally to manipulating a micro component by lifting, holding, and releasing the micro component while it is moved from an initial location to a destination location. It finds particular application in conjunction with fabrication of hybrid and complex microelectromechanical systems (MEMS). However, it is to be appreciated that the present exemplary embodiment is also amenable to manipulation of micro components for various purposes, including for other types of fabrication.
Advancements in MEMS technology have led to the design of MEMS devices with complex structures and geometries. MEMS devices are generally fabricated by well established monolithic micromachining where the micro parts are fabricated in one sequential process. However, more complex hybrid microsystems which have complex 3-D geometries and multiple micro components may use diverse materials and conflicting fabrication processes, and thus cannot be manufactured by monolithic micromachining. For these situations, microassembly is necessary to integrate various components into a complex functional system. Microassembly lies between conventional (macro-scale) assembly (i.e., part dimensions greater than 1 mm) and the emerging field of nanoassembly (i.e., part dimensions in the molecular scale, e.g., less than 1 nm). For additional information on microassembly, see Bohringer et al., Chapter 55 Microassembly, The Handbook of Industrial Robotics, 2nd ed. (Wiley, New York, Feb. 16, 1999), pp. 1045-1066, the contents of which are fully incorporated herein by reference.
One major focus of microassembly is microgripping and micromanipulation tools to accurately deliver and place micro parts or components in desired positions. Conventional microgrippers typically generate forces in the order of several Newton's during contact with the micro objects. This amount of force has a tendency to scratch or indent micro objects, and destroy critical features on the component during assembly. In addition, the assembly of micro parts using conventional mechanical microgrippers can be hindered by undesired surface adhesion between a micro part and the gripper, caused by surface forces such as electrostatic forces, van der Waals forces, and capillary forces.
Non-intrusive micro manipulation methods including optical tweezers, electro kinetic traps, and acoustic traps have been reported. For additional information on optical tweezers, see Grier, A Revolution in Optical Manipulation, Nature, Vol. 424, No. 6950, Aug. 14, 2003, pp. 810-816, the contents of which are fully incorporated herein by reference. For additional information on electro kinetic traps, see Chiou et al., Massively Parallel Manipulation of Single Cells and Microparticles Using Optical Images, Nature, Vol. 436, No. 7049, Jul. 21, 2005, pp. 370-372, the contents of which are fully incorporated herein by reference. For additional information on acoustic traps, see Shi et al., Focusing Microparticles in a Microfluidic Channel with Standing Surface Acoustic Waves (SSAW), Lab on a Chip, Vol. 8, Issue 2, 2008, pp. 221-223, the contents of which are fully incorporated herein by reference. Optical tweezers have been used to trap nanoscale particles, but cannot generate large enough optical forces to trap objects with weights in the pNewton order. Electro kinetic and acoustic traps, on the other hand, are only applicable to micro particles suspended in liquid. A review of the various handling principles used in microassembly is provided in Cecil et al., 2007, Assembly and Manipulation of Micro Devices—A State of the Art Survey Source, Robotics and Computer-Integrated Manufacturing, Vol. 23, Issue 5, October 2007, pp. 580-588, the contents of which are fully incorporated herein by reference.
Capillary and surface forces are insubstantial at the macro scale, but are dominant forces at the micro- and nano-scales and can be utilized as a gripping mechanism. Capillary grippers take advantage of capillary lifting force evolving from a liquid bridge between two surfaces. For additional information on capillary grippers, see Tichem et al., Capturing Micro-assembly Process Windows on Process Data Sheets, The 6th IEEE International Symposium on Assembly and Task Planning From Nano to Macro Assembly and Manufacturing, Jul. 19-21, 2005, pp. 74-79, the contents of which are fully incorporated herein by reference. One challenge for a capillary gripper is that, once an object is picked up, the capillary lifting force remains constant and the object is difficult to release. Many release strategies have been proposed to facilitate object release, including reducing the volume of liquid by evaporation or heating, tilting/sliding the gripper with respect to the object, using a hydrophobic (poly)tetrafluoroethylene (PTFE) auxiliary tool, releasing the object by positive mechanical engagement, injection of gas, and using mechanical needles. All these release techniques require external actuation apparatus and increase the system complexity. For additional information on release strategies, see Lambert et al., Design Rules for a Capillary Gripper in Microassembly, The 6th IEEE International Symposium on Assembly and Task Planning From Nano to Macro Assembly and Manufacturing, Jul. 19-21, 2005, pp. 67-73, and Bark et al., Gripping with Low Viscosity Fluids, The 11th Annual Int. Workshop on MEMS, Heidelberg, Germany, Jan. 25-29, 1998, 301-305, the contents of which are fully incorporated herein by reference.